1. Field of the Invention
The present invention relates to a work chucking/inserting apparatus and, more particularly, to a work chucking/inserting apparatus of simple structure capable of handling various sizes of works for alignment with and insertion into an insertion hole within a short time and with high working efficiency.
2. Description of the Prior Art
In inserting a work into an insertion hole with use of a machine such as a robot, conventional techniques correct a deviation between the position of the insertion hole and the present position of the work by using a jig for insertion or using a Vision (a two-dimensional visual device) to detect the position of the insertion hole.
For example, in the case where a jig for insertion is used (Japanese Patent Laid Open No. 115 129/84), as shown in FIG. 17, the inserting jig 01 has a through-hole with an inlet opening larger than an insertion hole 02. The through-hole tapers or gently curves inward and leads to an outlet (insertion port) which is of the same shape as the opening of the insertion hole 02 located on the side opposite the inlet of the inserting jig 01.
The inserting jig 01 having such a shape is first placed on the opening of the insertion hole 02 formed in an object (e.g., cylinder) 05 so as to be in approximate alignment with the insertion hole 02. At this time, the axis of the inserting jig 01 and that of the insertion hole 02 are not in exact alignment with each other. In this state, an expander 03 having plural fingers capable of expanding outwardly is inserted into the insertion hole 02 and then the plural fingers are expanded outwards. As a result, the inserting jig 01 moves and the axis thereof comes into alignment with the axis of the insertion hole 02 (see FIG. 18) and is fixed therein.
Next, a workpiece (e.g., piston) 04 is pushed in toward the insertion hole 02, following the tapered shape of the inserting jig 01, passing through the outlet of the inserting jig 01 and entering into the insertion hole 02 (see FIG. 19).
However, in such a conventional method which uses the inserting jig 01, it is necessary that the shape of the jig 01 be in conformity with the shape of the insertion hole; that is, it is necessary to provide a different inserting jig for each type of insertion hole. Besides, extra working time is required for the aligning work using the expander 03. Under these circumstances, in a multi-type mixed production line handling more than three types, the application of the method using the inserting jig 01 becomes difficult. For example, in an engine assembling line, an example of a multi-type mixed production line, the process of inserting a piston into a cylinder bore is in many cases carried out by manual operation.
Another known method using a jig is disclosed in Japanese Patent Laid Open No. 256526/92. In this later method a position detecting jig is moved in searching for the position of the insertion hole with use of a force control. In this method, however, a work chucking/inserting apparatus is required to shift the jig and a component from one to the other. This is time-consuming and a shift error occurs upon repetition of each such jig shifting operation. Methods which utilize similar tracing mechanisms are disclosed in Japanese Patent Laid Open Nos. 108108/93 and 168927/96, in which methods the position of an insertion hole is detected while allowing a work to contact and follow the insertion hole. But both methods involve problems such as the damage of components because the work itself is brought into contact with the insertion hole for detecting the position of the hole.
In using a Vision (a two-dimensional visual device), a positional deviation between a workpiece and an insertion hole is detected by the Vision, position data for a robot for chucking and conveying the work are corrected, and the work is inserted into the insertion hole at the exact robot position. However, the Vision is relatively expensive. Moreover, the accuracy of the measurement made by the Vision can be no higher than the resolution thereof, so for a highly accurate detection of the hole position it is necessary to take a close-up of the hole, requiring three or more cameras in the case of a large hole. Any attempt to enhance the accuracy results in a further increase in cost. Moreover, correction for matching both Vision and robot coordinate systems is troublesome and a complete matching is impossible, that is, the occurrence of error is unavoidable. Mechanical changes e.g., changes in weight and temperature, and shock, a change in illumination, or a change in optical conditions of the hole also give rise to error.